expresskeys: command not found

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH
/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin

If it's empty, You may set the PATH variable with this command

export PATH="/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin"

On CentOS possible default full paths are:

/usr/bin/expresskeys - from package: wacomexpresskeys

You may install the required package with command yum install {package}

Error in other languages:
expresskeys: bevel nie gevind nie
expresskeys: comandă negăsită
expresskeys: comando não encontrado
expresskeys: commande introuvable
expresskeys: command not found
expresskeys: käsku ei ole
expresskeys: không tìm thấy lệnh
expresskeys: komanda nerasta
expresskeys: Kommando nicht gefunden.
expresskeys: kommandot finns inte
expresskeys: komut yok
expresskeys: nie znaleziono polecenia
expresskeys: níor aimsíodh an t-ordú
expresskeys: no se encontró la orden
expresskeys: no s'ha trobat l'ordre
expresskeys: opdracht niet gevonden
expresskeys: parancs nem található
expresskeys: perintah tidak ditemukan
expresskeys: príkaz nenájdený
expresskeys: příkaz nenalezen
expresskeys: команда не найдена
expresskeys: командата не е открита
expresskeys: 命令找不到
expresskeys: コマンドが見つかりません